Cycloplegic and mydriatic eye drops are important dMuscles within the eye control the size of the pupil and the diameter of the ciliary ring. Drugs that cause an increase in the diameter of the pupil or dilatation are called as Mydriatics. Drugs that cause both pupillary dilatations, as well as cycloplegia (ciliary muscle paralysis), are called as Cycloplegics.
The ciliary ring in the contracted state is smaller in diameter and lens is in the accommodated state. It is larger in diameter when relaxed and lens is in unaccommodated.
The Pupillary pathways
Pupils are controlled by two muscles (Sphincter Pupillae & Dilator Pupillae). The sphincter is supplied by cholinergic nerves of the parasympathetic system through the third cranial nerve. The dilator pupillae muscle is supplied by the adrenergic fibers of the cervical sympathetic nerve.
Cycloplegics
- Used for evaluation & visualization of the posterior segment /Fundus examination
- The cycloplegic effect causes relaxation of accommodation
- Evaluation of hyperopia, refractive errors before refractive surgery, accommodative squints
- To release spasm of ciliary muscles as a result of inflammation.
- For prevention & release posterior synechiae in Uveitis.
- Dilatation and cycloplegia result in increased glare & photosensitivity, loss of depth perception and inability to focus near objects clearly. This effect depends on the type of drug used.
Mydriatics
Used for evaluation & visualization of posterior segment /fundus examination & lens mainly during eye Surgery
Mydriatic And Cycloplegic Cap Color
Mechanism of action:
- Mydriatics exert their effect on iris muscle
- No effect on ciliary muscle- accommodation
- All patients should be evaluated for anterior chamber angle depth before using mydriatics
- Patients should know the signs & symptoms of Acute angle closure glaucoma
- Should use sunglasses to avoid glare
Example of Mydriatic eye drops,
Phenylephrine Hydrochloride Ophthalmic Solution
- A sympathomimetic drug
- Selective alpha -1 agonist
- Acts on dilator fibers of Iris supplied by cervical sympathetic nerves
- Stimulates the dilator muscle of Iris
- Also causes blanching of conjunctival blood vessels
- Fast acting mydriatic
- The drug dilates slowly and pupil remains dilated for a longer time in people with darkly pigmented eyes
Indications of Phenylephrine
- Fundus and posterior segment examination
- It is also used to diagnose Horner’s syndrome where there is miosis in the affected eye; on instilling 1% phenylephrine in both of the eyes, the pupil in the affected eye — dilates more than the normal
Contraindications of Phenylephrine
- Narrow-angle Glaucoma
- Hypertension
- 10% conc. not to be given in infants
- Hypersensitivity
- Dose 2.5 and 10% conc. one – two drops
- Maximum dilatation- 30-40 minutes
- The effect lasts for 4-6 hrs.
- In infants 2.5 % conc. Is used along with other cycloplegics
- Side effects increase with higher concentrations
Topical use causes side effects like
- Stinging
- Blurred vision
- Increased BP
- Should be used with caution in patients with severe cardiovascular or cerebral disorders
- Blanching of the conjunctiva
- Mild widening of palpebral fissure due to stimulation of Muller’s muscle
CYCLOPLEGIC AGENTS
- Parasympatholytic drug (anticholinergic drug)
- Block the Iris sphincter & ciliary muscle
- Cause dilation of pupil and loss of accommodation or cycloplegia
Commonly used agents
- Atropine
- Homatropine
- Cyclopentolate
- Tropicamide
Used to know the correct refraction in children & adults who are hyperopic and before Laser refractive surgery. Also used to relax spasm of the ciliary muscle in anterior uveitis
Major side effects are
- Blurred vision
- Stinging of eyes
- Loss of near focus & Glare
ATROPINE SULPHATE 0.5%, 1%
- Available as a sterile ophthalmic solution
- Ointment and drops
- Is an anticholinergic agent
Mechanism of action
- Natural alkaloid
- Acts directly on muscarinic receptors of structures innervated by postganglionic fibers parasympathetic
- Is a competitive inhibitor of the muscarinic action of acetylcholine
- Strongest cycloplegic
- Causes abolition of light reflex
- Cycloplegia lasts for 7-10 days
- Ciliary muscle recovers earlier than the pupillary sphincter
- Has mild anaesthetic action on the cornea
- Atropine in the eye is absorbed through the cornea
Indications of Atropine Eye Drops
- Used as an ointment in children < 5yrs of age dose is three times a day for 3 days, retinoscopy is done at 4th day, PMT done at 3wks
- Cycloplegia and Mydriasis
- Pupillary dilatation in inflammatory conditions like anterior uveitis
- For prevention of synechia
- Relief of ciliary spasm(accommodative)
- Amblyopia-penalization therapy
Contraindications
- Narrow anterior chamber
- Narrow-angle glaucoma
- Hypersensitivity
- Use with caution in elderly with prostate hypertrophy
- Side effects of atropine
Poisoning can occur due to drug overdose resulting in:
- Dry mouth, difficulty in swallowing and talking
- Flushed & hot skin
- Fever
- Difficulty in micturition, a scarlet rash may appear
- Palpitation
- Excitement, psychotic behaviour, ataxia, delirium and hallucination
- Hypotension, weak & rapid pulse, cardiovascular collapse, respiratory depression
- Convulsions & coma in severe poisoning
Side effects
- Photophobia
- The blurring of near vision
- Allergic reactions locally around eyes—redness, crusting, wrinkling, conjunctival congestion
- Dryness of mouth
- Tachycardia
- Skin rash
- Abdominal distension in children
- Hypotension
- Respiratory depression
Peak effect- 2-3 days
Duration of action-10-20 days
PMT is done after 3 weeks
Tone allowance -1 D
Atropine substitutes
Semi-synthetic derivatives & synthetic alkaloids
Atropine has a slow & long lasting effect which is undesirable hence, other substitutes are used
HOMATROPINE 2% EYE DROPS
- It is less potent than atropine
- Used in patients between 5-8 yrs of age
- Its action starts in 30-60 minutes
- Action lasts for 1-3 days (mydriatic effect) & accommodation returns after 1-2 days
- PMT done after 3 days
- One drop is used every 10 minutes for six times
- Retinoscopy is done after 90 minutes
- Tone allowance 0.5D
CYCLOPENTOLATE 1% EYE DROPS
- Potent and rapidly acting mydriatic and cycloplegic
- Used in patients between 8-20 yrs of age
- The effect occurs in 30-90 minutes
- The effect lasts for 6-18 hrs
- One drop every 15 minutes for three times
- PMT did after 3 days
- Tone -0.75D
- Transient behaviour changes may be seen in children as a side effect
TROPICAMIDE 0.5%, 1% DROPS
- Has quickest & briefest action
- The effect starts in 20-40 minutes & lasts for 3-6 hrs
- Useful in adults for short cycloplegia
- One drop every 15 minutes for three to four times
